In recent years, computer systems have become a vital foundation for corporate activities. Even when a breakdown of a system happens due to, for example, a disaster, an important issue is to promptly restore the system to its normal condition. For example, there is a technique that guarantees consistency of data between a plurality of volumes by performing remote copying of the data from a host computer to a remote place in the order of writing data to each of a plurality of volumes belonging to one volume group in order to restore the system using the plurality of volumes to its normal condition. Furthermore, there is a technique that guarantees the consistency of data between volumes across a plurality of storage apparatuses (for example, see PTL 1).
Meanwhile, there is a technique that flexibly increases or decreases an amount of resources by coupling a plurality of storage apparatuses which have a function sorting read/write commands and management commands, and making the coupled storage apparatuses operate as a single virtual storage apparatus (for example, see PTL 2).